Manufacture of shadow mask color picture tube

ABSTRACT

The mask-frame subassembly of a color picture tube is made with the formed mask portion thereof imperforate and, therefore, a blank. Both surfaces of the blank are coated with a photosensitive resist and exposed through master patterns to create latent images of apertures to be formed in the blank. These images are developed and the mask blank is thereafter etched from both surfaces to produce an aperture pattern determined by that of the masters. The image area of the tube is screened through well-known photoprinting techniques in which a second master is employed to define and precisely locate the pattern of phosphor deposits. After screening, filming and aluminizing, the face panel section of the tube receives the aperture mask-frame subassembly and the tube processing then continues in conventional manner. In developing an aperture pattern in the mask blank and in screening the face panel, a system of studs and leaf springs or supports is employed to establish a coupling of kinematical design. This is characterized by unique positioning of the coupled elements with their geometric centers in a known reference location and makes possible interchangeability of masks and panels.

United States Patent Flore 1 51 July 18, 1972 1 MANUFACTURE OF SHADOWMASK COLOR PICTURE TUBE Joseph P. Flore, Chicago, [11,

[73] Assignee: Zenith Radio Corporation, Chicago, 111.

[22] Filed: May 1, 1970 [21] Appl. No.: 33,766

[72] lnventor:

Primary Examiner-John F. Campbell Assistant Examiner-Richard BernardLazarus Attorney-Francis W. Crotty ABSTRACT The mask-frame subassemblyof a color picture tube is made with the formed mask portion thereofimperforate and, therefore, it blank. Both surfaces of the blank arecoated with a photosensitive resist and exposed through master patternsto create latent images of apertures to be formed in the blank. Theseimages are developed and the mask blank is thereafter etched from bothsurfaces to produce an aperture pattern determined by that of themasters. The image area of the tube is screened through well-knownphotoprinting techniques in which a second master is employed to defineand precisely locate the pattern of phosphor deposits. Afler screening,filming and aluminizing, the face panel section of the tube receives theaperture mask-frame subassembly and the tube processing then continuesin conventional manner. In developing an aperture pattern in the maskblank and in screening the face panel, a system of studs and leafsprings or supports is employed to establish a coupling of kinematicaldesign. This is characterized by unique positioning of the coupledelements with their geometric centers in a known reference location andmakes possible interchangeability of masks and panels.

17 China, 16 Drawing figures Patented July 18, 1972 5 Sheets-Sheet lMoskBlonk Frome Forming Forming i i Oxidizing Oxidizing y SpringAhoching HQ 2 MoskBlonk Frome Assembling i Master Stress Poi'iernReiieving Phosphor Exposing 8 Screening Developing l V Oxide FilmingStripping 8i Erohing i i Aluminizing Blockening Mosk inserting InventorJoseph P Here AHorne Patented July 18, 1972 3,676,914

5 Sheets-Sheet l;

Patented July 18, 1972 3,676,914

5 Sheets-Sheet 3 Inventor 4 JosephPFiore AHorn Patented July 18, 19723,676,914

5 Sheets-Sheet i Inventor Joseph P. Fiore Attorney n u a. u u o o n In lu a a o n u u o- 5 Sheets-Sheet f Patented July 18, 1972 Attorneyiriventor Joseph P Fiore MANUFACTURE OF SHADOW MASK COLOR PICTURE TUBEBACKGROUND OF THE INVENTION The present invention is directed to animproved process for the manufacture of shadow mask color picture tubes.lt achieves a result that has long been desired, namely,interchangeability of masks and screen panels.

In processing tubes of the type under consideration, it is customary todetermine the pattern and precise location of the phosphor deposits onthe screen of the tube by exposing through the shadow mask a photoresistlayer or other sensitized coating that has been applied over the screen.Such exposure establishes a latent image of the phosphor deposits whichis then developed and, repeating this sequence each of three times,forms the familiar dot triads over the screen area of the tube. Eachsuch triad comprises a dot of green, a dot of blue and a dot of redphosphor.

It is of critical importance to the successful operation of such a tubethat the apertures of the mask, installed in the tube and through whichcolor selection is achieved, be in precise alignment or registry withthe dot triads of the screen otherwise color fringing or imperfectionsmay be experienced. This is such a necessary relation that it has beenobtained in prior manufacturing processes by temporarily installing agiven shadow mask within the face panel during each of the threeexposure steps of the screening process and by permanently positioningthe same mask within the panel when screening has been completed. Thispractice is known as pairing and has become widespread in the commercialproduction of shadow mask tubes. By pairing" is meant an assignment of aparticular shadow mask to a particular face panel section ofa tube. Asevere limitation inherent in pairing is that the mask is referenced tothe panel during screening and imposes its own peculiarities on thephosphor pattern of the screen structure. As a consequenceinterchangeability of masks and/or panels is impossible if colorimperfections are to be avoided. As a general proposition, thecOlor-selection electrode or shadow mask is a working part of the tubeand may not be compatible with screening requirements, as will becomeapparent presently in the discussion of black-surround andpost-deflection-focus types of color tubes.

While the pairing technique may be, and in fact is, used suc cessfullyin the commercial manufacture of shadow mask tubes, its limitations addto the cost, complexity and inconvenience of the manufacturing process.By way of example, if a tube has been completely screened and its masksuffers damage, such as denting or other deformation, all is lost andthe screen processing must be undertaken again from the very beginning.This follows simply because the screen of the tube made in accordancewith prior practices is uniquely identified with a particular mask andit is not feasible to substitute a different mask in the event of damageto the one that has been used in screening. A substituted mask will nothave the precision of matching or registration with the screen requiredto achieve acceptable color fidelity in image reproduction. It will beself-evident that interchangeability of masks provides dramaticeconomies in manufacture. By way of illustration, where suchinterchangeability is possible, if a given mask becomes damaged, anothermay be substituted in its place in the tube in process or, in otherwords, the screen may be salvaged. Other attractive advantages includesimplification in the screening process since screening may beaccomplished without having to insert and remove the shadow mask fromthe face panel section several times and also the mask may be keptcleaner which is highly desirable.

One form of shadow mask that has been recently introduced commerciallyfeatures phosphor dots of reduced diameter so that the dots are spacedfrom one another over the image area, rather than being in tangentialcontact as typified by the original commercial version of the tube. Inits more recent form, the tube has light-absorbing material disposed inthe spaces between, and on the screen area surrounding, the

phosphor dots giving rise to the popular description of a blacksurroundtube. A tube of this type is described and claimed in U.S. Pat. No.3,l46,368, issued on Aug. 25, I964 and assigned to the assignee of thepresent invention. The black-surround tube has decided advantages bothin respect of brightness and contrast. It is, however, a comparativelydifficult tube to manufacture particularly with regard to screeningsince it is necessary, in the preferred structure, to have the electronbeams of the tube larger in size than the phosphor dots constituting thedot triads of the screen. A similar requirement with attendantmanufacturing difficulties is presented with the so-calledpost-deflection-acceleration or focus type of shadow-mask tube. Wereinterchangeability of masks possible, and such is the contribution ofthe present invention, there is a very marked simplification in themanufacture of black-surround and post-deflectionfocus shadow-masktubes.

Accordingly, it is an object of the invention to provide an improvedprocess for the manufacture of shadow-mask color tubes.

It is another object of the invention to improve the manufacture of suchtubes by avoiding one or more of the aforementioned difiiculties ofprior processes.

it is a specific object of the invention to provide forinterchangeability of masks and/or panels in the manufacture of shadowmask color tubes whether they feature black-surround andpost-deflection-focus or not.

SUMMARY OF THE INVENTION The invention improves the manufacture ofshadow-mask types of color picture tubes through a process one embodiment of which includes the step of forming a mask-frame component orsubassembly from a material that may be etched. The formed mask isimperforate and is configured to correspond substantially to theinternal surface of the face panel section of the tube in process. Theframe portion extends from the mask portion for securing the mask-framesubassembly in a predetermined position within the face panel section.Preferably, the mask-frame subassembly is first thermally treated forstress relief and then a coating of a sensitized resist is applied to atleast one surface of the mask after which the mask-frame subassembly issupported in a predetermined alignment with a master pattern throughwhich the mask blank coating is exposed to actinic energy to establishin the sensitized coating a latent image of a desired aperture pattern.This latent image is then developed and thereafter the mask blank isetched to create the desired aperture patterns.

In a complementary operation, a master pattern is also used to screen onthe internal surface of the face panel section of the tube aninterleaved series of deposits of different phosphor materials arrangedwith the deposits of any given phosphor material distributed inaccordance with the aperture pattern that has been created in the mask.In screening, the panel is uniquely referenced to the master pattern,just as the mask blank was referenced to its master pattern indeveloping apertures in the mask, in order to achieve interchangeabilityof masks and panels. Finally, and after the screening has beenaccomplished, the mask-frame subassembly is installed in the face panelsection of the tube.

In one specific and preferred embodiment of the invention the aperturepattern formed in the mask portion of the maskframe subassembly isdetermined by the master pattern but the relative sizes of the holes inthe master and in the mask is determined by whether or not the screen isconventional or is to be for the black-surround or post-deflection-focusvariety of shadow-mask tube. If it is of either the last two mentionedvarieties, the individual apertures formed in the mask portion of themask-frame subassembly are larger than those of the master pattern andare also larger than the phosphor deposits formed by screening the facepanel with its master. Control of the mask aperture size in relation toits master and in relation to the phosphor dots of the screen is readilyattained by adjustment of parameters of the exposing step as well beexplained.

BRIEF DESCRIPTION OF THE DRAWINGS The features of the present inventionwhich are believed to be novel are set forth with particularity in theappended claims. The invention, together with further objects and advantages thereof, may be best understood by reference to the followingdescription taken in connection with the accompanying drawings, in theseveral figures of which like reference numerals identify like elements,and in which:

FIGS. la-lc are sketches used in explaining a particular type ofmechanical coupling system used in practicing the sub' ject invention toattain interchangeability;

FIG. 2 is a flow chart of process steps taken in the manufacture of ashadow mask color tube in accordance with the invention;

FIGS. 3a and 3b are sketches pertaining to mask and frame assembling;

HO. 4 is a sketch used in explaining a method of developing masterpatterns to be employed in preparing an aperture mask;

FIGS. Sa-Sd are detail but fragmentary views of process steps forforming an aperture pattern in the mask of the tube in process; and

FIGS. 6-7 are sketches pertaining to master pattern forming for, and foruse in, screening.

Shadow-mask tubes come in a variety of sizes and shapes with phosphordeposits that may likewise be of different shapes. For example, a tubeof a given screen dimension may be round or rectangular and the variousphosphor materials may be applied in the form of strips or dots.Practice of the present invention is not dependent on such factors andit will be assumed, simply for convenience, that the tube underconsideration is a 23-inch rectangular tube for which the screen is amultiplicity of phosphor clot triads distributed over the image area ofits face panel section.

Structurally, tubes of the type in question are formed of envelopes thathave two principal parts; a face panel section and a funnel section. Theface panel section is rather like a flanged dish with a skirt or flangecircumscribing a screen or image area which is to be screened withphosphor materials. For the additive type of color television systemcurrently in commercial use the screen is a repeating pattern or aninterlace of similar deposits of green, blue and red phosphor materialscollectively defining phosphor dot triads. The funnel section has anenlarged end which matches, both as to dimension and configuration, theflange of the face panel section so that they may be sealed together bymeans of a sealing frit to constitute an envelope suitable forsupporting a vacuum. The small end of the funnel section accommodates aneck which houses at least one electron gun but usually a cluster ofthree such guns is arranged to develop three electron beams that aredirected and accelerated toward the screen of the tube. With the tubeassembled, the shadow mask is interposed between the gun cluster and thescreen, being very much closer to the latter. The apertures of the maskpermit color selection by confining each of the three electron beams toimpinge upon only the particular phosphor material to which any givenbeam has been assigned. In these respects the structure and operation ofthe tube are entirely conventional and need not be discussed in furtherdetail.

The improved method of manufacturing shadow mask tubes has the desiredattribute of interchangeability of shadow masks and face panels andcomprises two series of processing steps that may progress independentlyof one another. One is forming of the mask-frame subassembly of the tubeand the other is screening its image area. They will be considered inthe recited order but first the matter of interchangeability deservescomment.

Let it be assumed initially that the mask-frame subassembly is preparedin the manner presently to be described to achieve interchangeability sothat any one of a production lot is suitable for installation in a giventube being fabricated. Let it be further assumed that screening isperfonned in the conventional way except that a master mask, properlyrelated to the mask-frame subassembly in respect of its aperturepattern, is temporarily installed within the face panel for each of therequired three exposures utilized in defining the phosphor deposits thatcollectively constitute the image screen. In this case,interchangeability will be true of masks only and not of panels because,in the screening process, the exposure mask will have been referenced tothe panel rather than to a reference that is meaningful to themask-frame subassembly. Only half of the desired ultimate objective willhave been attained. Preferably, in screening the panel is uniquelyreferenced to the master rather than vice versa so thatinterchangeability of panels as well as masks is achieved. The desiredobjective is accomplished by the use of a coupling system of kinematicaldesign through which unique referencing is established in processingboth the mask blank and the image screen of the face panel.

An understanding of such a coupling system may be derived from aconsideration of FIGS. 10-11 in which it is assumed that a mask,represented by rectangle B, is to be uniquely cou pled and referenced toa face panel, represented by rectangle A, with their geometric centerssuperposed. A pair of locating pins 1 and 2 is first secured to one faceon panel A at a distance x/Z from its horizontal centerline, where x isthe height of mask B. A third locating pin 3 is affixed to the same faceof panel A at a distance y/2 from its vertical centerline, where y isthe width of mask B. These three pins establish a fixed or uniqueorientation if mask B is placed on panel A with three points of itsperiphery contacting pins 1-3 but the planar relationship of bodies Aand B will not have been determined. For that purpose, three identicalpads 4-6 are affixed to the same face of panel A to receive and supportthe periphery of mask B. With these pads in place, the bodies A and Bare coupled with uniqueness as to planar position and orientation andthis has been accomplished with six points of contact or coupling. Sixis at once the minimal and adequate number of points to determineuniqueness and, while additional locating pins and pads may be employedfor added mechanical strength, they are redundant so far as positioningis concerned. Of course, any added pins or pads must be compatible withthe positioning established by the aforesaid six points.

Equivalent results may be obtained through the use of three couplingconnections each of which provides two of the necessary six points, asexplained in the text Procedures in Experimental Physics by John Strong,Prentice-Hall 1939 at page 585. It will be recognized that the leafspring-stud coupling arrangement conventionally employed in shadow maskcolor tubes is of this type since the studs projecting inwardly of theface panel to support the mask are circular in cross section and theapertures provided in the leaf mounting springs of the mask aretriangular in shape so that when received by the mounting studs eachleaf spring and stud coupling defines two support points andcollectively the three constitute the six points required foruniqueness. While prior tube structures utilize this kind of couplingarrangement, their processing has not been carried out in the mannernecessary to achieve interchangeability. A novel process to secure sucha result will be explained but attention is first directed to formingthe maskframe subassembly.

To a considerable extent the mask-frame subassembly is manufactured inaccordance with the method described in US. Pat. No. 3,35 l ,996, issuedon Nov. l4, I967 and assigned to the assignee of the present invention.There is one most significant difference, however, in the two methodsand it is this difference which makes interchangeability of masksrealizable, whereas the method of the earlier patent is directed tomasks used in the practice of pairing alluded to above. Moreparticularly, the mask-frame subassembly of the patent features theformation of an apertured mask which is then united with a frame whilein accordance with the present invention a mask blank which isimperforate, except possibly for locating holes in its peripheralportion, is formed with a frame after which the subassembly is furtherprocessed to develop a desired pattern of apertures in its mask. It isknown that the mask and frame may be formed from a single blank ofmaterial or they may be fabricated separately and then combined in asubassembly. Either approach is acceptable although the latter isdepicted in the flow chart of FIG. 2. Accordingly, a mask blank ofsuitable material is first formed to the configuration desired of themask as used in the tube. The material chosen is one that lends itselfto chemical milling, as by etching, and is usually a thin sheet ofannealed steel of approximately 5 mil thickness. The blank is cut to adesired shape, that is to say, round or rectangular but rectangular forthe case under consideration, and is heat treated and work hardenedpreparatory to being pressed into a desired form. Since the internalsurface of the panel section of the tube is approximately a sphericalsection, the mask blank is given a similar configuration so that themask, when finally positioned within the tube is in essentially parallelrelation to the screen, that is to say, these components are positionedin parallel or in nested concentric relation. The mask may be diepressed or drape drawn in accordance with the apparatus and method ofU.S. Pat. No. 3,296,850 issued on Jan. 10, 1967 and assigned to theassignee of the present invention.

Having formed the mask blank into a spherical section, it is degreasedand blackened or oxidized to have radiation properties similar to thoseof a black body. A variety of processes are available for this purposeincluding chemical blackening and thermal blackening, the latter beingaccomplished by heating the mask blank for an appropriate period oftime. For example, the mask may be heated to 600 degrees F. and theoxygen of the oven then purged and replaced by steam. The temperature isthen increased to 1,000 degrees F. and retained for about minutes tooxidize or blacken the mask in an oxidizing atmosphere. An attractiveadvantage derived from thermal blackening at high temperature is addedstability or contour control of the mask through stress relieving, thatis to say, stresses that may have been introduced in the mask-blankforming are relieved by heat treating. Experience reveals that stressesin the mask after the mask-forming operation are responsible forinstabilities and undesired changes in the mask contour leading to colorcontamination in the finished tube. This is avoided by stress relievingof the mask which is to be accomplished before joining the mask to itsframe. Stress relieving may result from thermal oxidation or may beundertaken as a separate process step but in any event it is to beaccomplished in preparing the mask for uniting with a frame.

The formed but imperforate mask blank is to be provided with a frame sothat the mask-frame subassembly may be mechanically and permanentlypositioned within the panel section of the tube. As stated above, theflow chart of FIG. 2 contemplates forming the frame separately as bystamping from a sheet of cold rolled steel that is relatively thick andtherefore mechanically much stronger than the mask. Typically, the frameis formed of 93 mil stock and it is dimensioned and configured inrelation to the mask blank to facilitate their being assembled intelescoping or overlapping relation after which they may be welded toone another. One method of preparing the frame with its mounting springsis disclosed in U.S. Pat. No. 3,351,996 referred to above. Briefly, aframe of appropriate dimensions is stamped from a blank of steel and isthen stamped or otherwise shaped into a desired configuration foruniting with the mask blank.

in accordance with another well-known method, the mask frame is formedfrom strip stock through a roll and forming process. After shaping, theframe preferably is stress relieved which may be done at a hightemperature with a short time cycle or at a relatively low temperaturebut with a long time cycle. Assuming the frame material to have anannealing temperature of about L600 degrees F., stress relieving may beachieved by heating to L400 degrees F. for approximately minutes.

The formed frame is oxidized, as indicated in FIG. 2, and is thenprovided with leaf springs which are attached to the frame at one endand present triangularly shaped mounting apertures at the opposite enddimensioned to receive mounting studs projecting inwardly of the facepanel section of the. tube to support the mask-frame in position. Thereare three or four such mountinG springs depending upon the choice thatis made as between a three and four point suspension system. Asexplained, three are sufficient to the desired kinematical design and afourth may be used but it must be compatible to the design created bythe other three. For convenience, a three point suspension will beassumed. Of course, the overall dimensions of the mask-frame are lessthan the internal dimensions of the face panel to facilitate installingthe mask in position. Accordingly, the mounting springs are shaped toextend away from the frame to which they are attached and to bridge thedistance between the frame and the internal wall surfaces of the facepanel. The chart of FIG. 2 indicates that the mounting springs areattached to the frame prior to assembling of the mask-frame subassembly.One may, if desired. attach the springs after the mask-frame subassemblyhas been prepared, but there is distinct preference to attaching thesprings prior to fabricating the subassembly.

The sketch of FIG. 3a illustrates a preferred method of springattachment, assuming that three leaf springs are to be employed. Afixture is provided having three studs 15 that are dimensioned andpositioned to simulate a bogey face panel, that is to say, a panel whichis perfect as to configuration and dimension of its component parts. Thegeometric center of the simulated panel is indicated by the cross in thefigure. All three preformed leaf springs 14 are first assembled ontostuds 15 by means of the triangular openings in the springs with thelongitudinal axes of the springs coplanar with the axes of the studs.The frame B is now moved into position between the ends of springs 14which are then welded to the frame. Experience shows that this operationmay be conducted fast and with precision, assuring that the geometriccenter of frame B, coincides with that of the aforementioned simulatedpanel. Again, the kinematical coupling is relied on in achieving thedesired relation or unique positioning of the frame to a simulated bogeypanel.

The schematic diagram of FIG. 3b represents a formed but imperforatemask blank B, supported on a stationary bed 2 having a seat whichmatches the mask blank in conformation and suitable locating orpositioning devices (not shown) for orienting the mask blank. A frame8,, constructed in accordance with U.S. Pat. No. 2,897,392 issued July28, i959 and assigned to the assignee of the present invention, andhaving mounting springs 14 attached as just described, is shown abovemask blank 8,. Once again a fixture is used, having studs [5 to simulatea bogey panel and to receive leaf springs 14 of the frame. In formingthe mask-frame subassembly, frame B telescopes with reference to theflange of mask blank B, and when in position with its mounting springs14 engaging studs 15 its reference axis C coincides with reference axisD of the fixture, establishing a desired predetermined distance E fromthe crown at the center of the mask blank to the reference axis C offrame 8,. The telescoped parts are united by spot welding. This is a farmore precise and manageable dimensioning procedure than is available ifthe springs are attached after the subassembly has been constructed.

in any event, the mask-frame subassembly with the mounting springs inposition is made thermally stable by undergoing a final stress relievingstep. This is particularly beneficial because, whether the telescopedmask and frame are in perfect alignment or suffer some slightmisalignment in assembling, it is found that due to the difference inmass of these parts a stress condition is set up in the mask blank inthe area close to and per force of the individual welds. Unless relievedby thermal treatment, such stress results in deformation or unwantedchange in contour of the mask and color imperfections during tubeoperation. On the other hand, if the stress is relieved by heating toapproximately 470 degrees C. for about 10 minutes, the mask exhibits itsdesired contour in stable operation of the tube, as required foroptimized color reproduction. Accordingly, after the subassembly hasbeen made, it is stress relieved to cause the mask-frame subassembly tobe stable at temperatures encountered both in the succeeding processingsteps of the tube and in its operation in the reproduction of images insimulated natural color.

Oxidizing of the mask-frame subassembly, whether the components thereofare treated separately as described or after the subassembly has beenmade, further contributes to thermal stability in the operation of thetube. It is known that a significant portion of the electrons in thethree beams of the tube impinge upon and are intercepted by the mask. Asa consequence, the mask experiences a substantial increase in ternperature and may dissipate as much as 45-50 watts. Stability of thestructure in the face of such heat dissipation is enhanced by theoxidizing which causes the structure to have heat radiation propertiessimilar to those of a black body.

The next step in the processing of the mask-frame is to provide in theformed mask blank a multiplicity of apertures of a desired shape, sizeand location to define a pattern of apertures appropriate to theoperation of the tube in process. Since the tube under consideration hasbeen assumed to be a rectangular tube with a dot-triad type of screen,the mask is to be provided with circular apertures distributed in arectangular field. The mechanics of providing an aperture pattern in amask blank, as such, are quite well known and include the steps ofexposing and developing an image of the aperture pattern on the maskblank. For the process under consideration the exposure is through amaster pattern by means of which the specifications of the aperturepattern of the mask are precisely determined. It is appropriate, for thesake of completeness, to consider an acceptable process for preparingsuch a master for exposing mask blank 8,.

The sketch of FIG. 4 represents an exposure system by means of which abogey mask 8 is utilized in preparing a pair of masters M, and M to beused in developing aperture patterns in mask blanks which patternsaccurately duplicate that of bogey mask B. The expression bogey mask" ishere used to mean a mask with an aperture pattern that is optimum forimage reproduction with a bogey screen in which the three dif ferentphosphor materials have been deposited to form a multiplicity ofphosphor dot triads. It will have apertures of a desired sizedistributed over a rectangular field with uniform diameter or with agraded hole size, as desired. In many instances the hole size decreaseswith radial distance from the center of the mask.

The sketch of FIG. 4 shows bogey mask 8 supported by a fixture similarto that described in connection with FIG. 3a having studs dimensionedand positioned to simulate a bogey panel. These studs couple with theleaf mounting springs 14 of the mask B and support that mask in auniquely determined position with its geometric center and that of thesimulated panel disposed on the vertical axis of an optical projectionsystem. Two additional support systems of kinematical design, verysimilar to that of FIG. 1c, are arranged on opposite sides of fixture 15for the purpose of holding planar plates 17 and 17' of glass or the likein preselected exposure positions at chosen distances from bogey mask Band with their geometric centers aligned with that of the mask. Theaxial spacing of plates l7, 17' from mask B is not critical, it isselected from convenience and the parameters of the exposure step areadjusted to achieve a desired relation of the patterns M, and Mestablished on plates 17 and 17' respectively, in respect of theaperture pattern of mask B. The coupling systems for plates l7, l7individually have elements l6, 16' which may be similar to the pin andpad arrangement of FIG. la to be of kinematical design assuring that thegeometric cen ters of the mater blanks are aligned on a common axis withthat of bogey mask B.

The optical system of the exposure chamber represented by FIG. 4includes a pair of light sources S, and S, as well as a curvilinearlight reflector R. The reflector is constructed to the end that lightsource S, is imaged at point S, and vice versa, that is to say, and asrepresented by the broken construction lines of FIG. 4, a light rayissuing from source 8,, if permitted unimpeded travel to reflector R isreflected therefrom to the point 5,. And, likewise, a light ray fromlight source S, under the same conditions is reflected to the point 3,.

Each of plates I7, 17' bears a photosensitive coating on the surfacethereof facing mask B and the coating may he a positive resist which hasthe property that, upon exposure to actinic energy, such as ultravioletlight from source S, or 8,, it is rendered soluble, whereas it isotherwise insoluble in a particular solvent. The exposure process forcreating master patterns M, and M, is as follows: The blank 17' formaster pattern M having been coated with a light sensitive resist. isplaced on supports 16'; the blank I! for master pattern M, istemporarily removed from the projection system and light source S, aloneis energized. Accordingly, an image of the aperture pattern of mask B isprojected on the blank 17', creating therein a latent image of thedesired master pattern M The blank 17' is now removed from the exposurechamber and the latent image is developed by washing with a solvent ofthe resist. Having thus prepared master pattern M plate 17 is installedin its coupling system 16 and light source S, is energized. The lightfrom source S is projected from reflector R through mask B to blank 17and a latent image of master pattern M, results. The plate is removedfrom the exposure chamber and treated with a solvent to develop masterpattern M The described system features straight through projectionsince light sources S, and S, are imaged on one another and as aconsequence master patterns M, and M not only accurately represent theaperture pattern of bogey mask B, but also are properly related to oneanother in position. It is noted in passing that Eastman Kodak Companymarkets graphic art plates that are sensitized and directly useable asplates l7 and 17.

Having prepared master patterns M, and M their use in the continuedprocessing of the mask frame will be considered. If apertures are to beformed in the mask blank by etching from but a single side, it is onlynecessary to apply the photo or light sensitive coating to that side orsurface of the blank, although it is preferred that both surfaces of themask blank be coated and that etching be accomplished from both sides.Accordingly, both sides of the mask blank are coated with aphotosensitive resist of the type which experiences a change insolubility upon exposure to actinic energy. Resists are either of thenegative type which become insoluble in a solvent upon exposure or ofthe positive type which is normally insoluble but becomes soluble uponexposure. Either is suitable so long as the aperture pattern isprojected from a positive or negative image chosen to meet thecharacteristics of the resist. It is convenient to use a positive resistwhich is normally insoluble in a solvent but which becomes soluble uponexposure to ultraviolet light. Resists of this character arecommercially available; a typical one is Azo Plate Ill, distributed byShipley Company Incorporated of Newtown, Massachusetts. The coatedmask-frame is installed in the exposure chamber of FIG. 4 along withmaster patterns M, and M, and in substitution for bogey mask 8. Sincethe mask-frame in process is equipped with leaf mounting springs 14,identical to those of bogey mask 8, their coupling with studs 15 in thechamber supports the mask-frame in a unique exposure position which isprecisely the same as the position previously occupied by bogey mask B.By virtue of the uniqueness in position, established through the use ofa coupling system featuring kinematical design, the mask-frame isproperly referenced as required for interchangeability. Its geometriccenter is positioned where the geometric center of bogey mask B waslocated in preparing master patterns M, and M Now, both light sources 5,and S, are energized, or alternatively they may function in sequence, toexpose the concave surface of the mask-frame to master pattern M, and toexpose the convex surface thereof to master pattern M Further details ofthe mask-frame processing are represented by the fragmentary views ofFIGS. Sa-Sd.

FIG. 5a shows a fragment of mask blank B, with oxidized layers 12 and onits opposing surfaces and superposed layers or coating 13, 13a of apositive photosensitive resist.

The coating may be applied in any of a variety of ways such as flowcoating, spraying, dipping and spinning, electrostatic spraying, etc.After the coating has been applied and dried, the mask blank is exposedthrough master patterns M and M,, as explained above, which determinethe nature of the individual apertures and the aperture pattern to bedeveloped in the mask blank.

It may be noted in passing that there is flexibility in the exposurestep and in the master pattern utilized at the exposure step. While themask blank to be exposed has been preformed to a spherical section, themaster may be planar or other shape with its pattern of transparentportions and the optics of the light projection system arranged toproject the desired image on the mask blank. For example, it may beconvenient to form the master as a spherical section in order that itmay be positioned essentially in nested concentric relation with themask blank, between the light and mask blank during the exposure step.In the simplest case, where the mask blank has a single surface coatedwith a sensitized resist, the coating preferably is on the concave sideand the blank may be supported above the master mask in an exposurechamber or lighthouse similar to that customarily employed inphotoresist screening. Such a structure is described in US. Pat. No.3,319,556, issued on May l6, I967, and assigned to the assignee of thepresent invention. Preferably, however, both surfaces of the mask blankbear a sensitized resist and it is exposed in a chamber like that ofFIG. 4 so that both surfaces of the blank are exposed through the pairof master patterns M and M to establish latent images concurrently orsequentially, as desired, on both surfaces of the mask and inregistration with one another.

Where the aperture mask is for a screen having a mosaic or triadarrangement of phosphor deposits, as has been assumed, the exposed areasof the sensitized coatings for each hole of the mask are as representedin FIG. 5a, wherein the concave surface of the mask blank has an annularelemental area l4 exposed through a hold of master M in coaxialalignment with a similar but larger area 140 on the obverse surface ofthe blank exposed through the corresponding hold of master M Theseelemental areas represent latent images of apertures that are to bechemically milled, by etching, in those portions of the blank surfaceswhich they overlie. Image 14a is made larger than image 14 simplybecause etching is more easily undertaken through the use of images ofunequal size. These latent images 14, 14a are developed by washing themask with the solvent of the sensitized material of coatings 13, 13a asa consequence of which the exposed elemental areas wash out, leaving inthe coatings on the surfaces of the mask blank pairs of openings 15,150. There is a pair of such openings for each aperture to be formed inthe mask and the members of each pair are in registration with oneanother, that is to say, they are in radial alignment as illustrated inFIG. 5b. Having developed the series of openings I5, 150 in thesensitized coatings, the mask is heated to a temperature ofapproximately 250 degrees C. for 5 minutes in order to bake theremainder of the resist coatings.

The mask is next treated with a chemical stripper, as by flushing,dipping or spraying, for the purpose or removing the elemental portionsof oxide layers 12, 120 which lie immediately under or are exposedthrough openings 15, 15a of the resist coatings. The stripper employedmust be effective in removing oxide from the mask blank but it must notattack the residue of coatings 13, 13a. Hydrogen chloride is anacceptable stripper. It is desirable to strip the exposed portions ofthe oxide surfaces to facilitate etching since the oxide layers I2, 120otherwise serve as a resist which is relatively insensitive to theetchant and impedes etching. After having stripped the exposed portionsof the oxide layers, mask B is in the condition represented in FIG. 5cand is thereafter etched to develop the holes, such as hole 16 of FIG.5d in the mask blank. For the usual mask material etching is readilyaccomplished with ferric chloride acid that is applied by spraying ordipping into a tank in which the etchant is circulated by ultrasonicaction to improve uniformity of the etch. It is clear from the shape ofaperture l6 that the blank preferably is etched from both surfaces. Theconvex side of the mask blank which has coating 13a is etched first todevelop a large recess in blank B which does not break through theopposed surface, namely, that which bears resist coating 13. Etchingfrom the obverse or concave side of the blank through opening l5 thencauses aperture 16 to extend totally through blank 11 and determines itseffective diameter d. The large diameter section of aperture 16 may beformed relatively quickly and removes the major portion of the elementalpart of the mask blank required to mill aperture l6. The next etchingstep performed through opening 15 removes a minor part of the mask blankand, therefore, may be conveniently undertaken with adequate care andcontrol as required to precisely dimension the hole diameter d.

The effective size d of blank aperture 16 is dictated by the characterof the tube in process and is subject to control by adjusting thegeometry of the exposure system. For the conventional shadow mask tubewherein the phosphor dots are in tangential contact with one another,all over the image area. the hole diameter d is relatively small toconstruct the electron beams passing through apertured mask B, to adiameter less than that of the phosphor dots. On the other hand, wherethe tube is of the black-surround or post-deflection-focus variety, thehold diameter d is comparatively large since for this case. as explainedabove, the electron beam is larger in diameter than the phosphor dots. Agiven set of masters M and M may be used in forming the aperture patternin mask blank B for either type of tube. It is simply a matter ofadjusting the process parameters so that the latent images 14, 140formed on resist coatings [3, 13a by exposure through the masterpatterns are properly dimen-sioned.

In milling apertures 16 in mask blank 8,, the etchant attacks only theelemental surfaces of the mask blank that are exposed by holes 15, 15abecause the other surfaces of the mask blank are protected by theresidue of resist coatings 13, 13a. This is most advantageous in that aminimum of material is removed from the mask blank and that which isremoved is confined to those elemental portions of the blank where it isdesired that the apertures be formed. In other words, the mask retainsmaximum mechanical strength. When the etching has been completed, resistcoatings 13, are removed by washing the mask with a solvent for theresist. For positive resists trichlorethylene is a suitable solvent andfor negative resists, such as polyvinyl alcohol or fish glue, a causticsolution may be used. Now only the wall surfaces of apertures 16represent exposed surfaces of the mask; the remainder of the mask blankis covered by oxide layers I2, 120. The apertured mask is then subjectedto a chemical blackening which blackens the surfaces of the mask thathad been exposed as a consequence of etching. This restores to the maskthe black body properties that are desirable for heat dissipationpurposes. The mask shall now have been completely processed and themaskframe subassembly is in condition for final installation into a facepanel section of a shadow mask tube.

Of course, the face panel section of the tube in process must bescreened before the mask-frame subassembly is to be installed. Screeninghas in common with the described process of forming the mask-frame, thestep of exposing a sensitized layer or coating with actinic energydirected thereto through a master pattern but now to create a latentimage of phosphor dots instead of a latent image of mask apertures. Byexposing a sensitized layer that has been applied over the image area ofthe tube with a master pattern properly related, in specification andposition relative to a fixed or known reference, to that employed indeveloping a pattern of apertures in the mask blank, as described above,the desired feature of interchangeability is attained. Consequently, theflow chart of FIG. 2 indicates that the master pattern is utilized inmask blank processing as well as in phosphor screening.

Here, again, there is process flexibility but at the sacrifice of somedegree of interchangeability. More specifi-cally, in screening the facepanel a plate bearing a master pattern, such as plate 17, may beequipped with mounting springs so that the master may be temporarilyinstalled within the panel for the exposure step. Where this procedureis adopted, the master becomes referenced to the panel rather thanhaving the panel referenced to a bogey mask or other fixed reference. Asa con sequence interchangeability of panels is not achieved butinterchangeability of masks is retained since, as explained, the maskblanks are all properly referenced to a bogey panel during the exposurestep of mask-aperture forming. The preferred practice is to referencethe panel to a bogey mask in screening to the end that completeinterchangeability of masks and panels results. Before describing thescreening steps, a procedure will be given for developing a series ofmaster patterns for screening, appropriately derived from the same bogeymask B from which master patterns M and M, used in processing mask Bwere derived.

The apparatus employed is that of FIG. 6a which represents what is knownin the tube art as a demountable and may be thought of as a simulatedpicture tube, differing therefrom in two material respects. First of allthe envelope has a funnel portion 20 and a cap or face panel 21 that arenot sealed to one another. Instead, they may be assembled on a temporarybasis through a sealing joint well known to the art which so couples thecomponents that the envelope may hold a vacuum essentially the same asthat established in a finally evacuated picture tube. For thedemountable this is accomplished by a connection 22 to a vacuum systemwhich maintains the desired condition within the envelope. The small endof en velope section 20 has the usual gun cluster 23 and terminal base24 through which operating potentials are applied to the electrodesystem of the device. Of course, a high voltage connection (not shown)is also provided for the purpose of applying final anode voltage of theproper value. In order to scan with the electron beams issued from guncluster 23 a bogey yoke 25 is associated with envelope section 20 andthe other accessories, including static and dynamic convergence are alsoprovided. They constitute no part of the present invention and are wellknown so that for simplicity they have not been indicated in the sketch.Within the demountable there is supported a fixture again having studs Idimensioned and positioned to simulate a bogey panel. The same bogeymask B used in preparing masters M, and M described in connection withFIG. 4, is shown in position within the demountable, being supported inthe usual way by its mounting springs 14 engaging fixture studs 15.Another fixture having studs I6 supports a conductive plate 18, againthrough a coupling arrangement of kinematical design so that thegeometric centers of mask B and plate 18 are superposed or aligned alongthe electron optical axis of the demountable. The surface of plate 18facing gun cluster 23 is covered with an electron sensitive coating,such as polyvinyl alcohol sensitized with ammonium dichromate.

With bogey mask B and plate 18 in position and with panel 21 removablysealed to the free end of envelope section 20, a vacuum is drawn in thedemountable and the electrode system is energized so that electron beamsmay be developed. Three master patterns are required for screening, onefor each color, and while processed individually the same steps areinvolved for each. Assume that the master pattern under discussion isfor screening with green phosphor. In that case, only the gun of cluster23 that corresponds to the gun of the tube in process assigned to excitethe green phosphor dots of the screen is energized to issue an electronbeam that is accelerated toward plate 18 and is permitted to reach thereby traversing holes of bogey mask B. Concurrently, deflection signalsare applied to yoke 25 and the electron beam scans a bidirectionalraster on the mask to, in effect, project its aperture pattern onto theelectron sensitive coating of plate [8, creating therein a latent imageof that pattern. Thereafter, the vacuum is released, the demountable isopened and plate I8 is removed and rinsed with a solvent for its resistcoating to develop the latent aperture pattern.

The next step, illustrated in the sketch of FIG. 6b, is simply areduction of the aperture pattern established on plate IS in itstransfer to another plate 18' in well-known fashion. There are tworeasons for this image size reduction. Firstly, the distance 0 in FIG.6a shows that plate 18 is spaced from bogey mask 8 in its exposure stepby approximately the same distance that separates the mask from theimage screen in the finished tube. Additionally, this reduction step mayadjust for whatever position is desired of the screening master, betweenthe light source and face panel, during the exposure step incident toscreening with green phosphor.

The third step to be taken, as indicated in FIG. 6c, is projecting theimage pattern from plate I8 onto a final green master pattern M by meansofa light source S:, and a correcting lens L which corrects for the factthe plates used in developing screening master M are planar whereas thescreen surface of the face panel is a spherical section. This type oflens correction is well understood in the art and no difficulty would beexperienced in designing a suitable lens for making the surfacecurvature correction under consideration. It is highly beneficial anddistinctly preferred to employ a system of optical correcting lenses toimpart to the master M all of the correcting or compensating effectswhich, under prior art practices, are introduced by means of correctinglenses in the screening exposure chambers. By preparing master M toincorporate such corrections in its aperture pattern, the master may bepermanently installed in the screening exposure chamber and thecorrecting lens heretofore required in such chamber may be eliminated.Master pattern M may be used in screening with green phosphor but in anyfactory production a number ofexposure chambers are concurrently in usein screening face panels with green phosphor and, accordingly, a numberof duplicates of master pattern M are produced by contact printing. Onesuch master pattern is permanently installed in each exposure chamberutilized in the exposure step for processing with green phosphor.

A master pattern M for use in screening with blue phosphor is preparedin the same way and is duplicated for permanent installation in the blueexposure chambers. One difference in procedure is required, namely, thegun ofcluster 23 of the demountable to be energized in preparing masterM is the one which corresponds to the gun of the tube in processassigned to excite blue phosphor dots. In like fashion, a screeningmaster M for processing red phosphor is prepared and duplicated. In thiscase, the red gun of cluster 23 is energized and the remaining two arecut off.

Having prepared three master patterns M M M they are used in screeningwith their respective color phosphors in a process that is very similarto the prior art. Since the same process is practiced for each of thethree different phosphor materials, it is sufiicient to consider onlyone in detail and this will be done in relation to the sketches of FIGS.7a and 7b. The arrangement represented in FIG. 7a is the exposurechamber for green and has the usual source 30 of ultraviolet light whichmay expose the facepanel P of a tube in process through master pattern Msupported between the light source and the panel. It will be observedthat no correcting lens is included in the exposure chamber. Again, topreserve condi tions necessary to interchangeability of panels, masterpattern M and panel P are engaged by coupling systems of kinematicaldesign by which reference positions are established. More particularly,couplings 16 support the master pattern with its geometric center alongthe optical axis of the chamber. Similarly the support for panel Pestablishes its geometric center along the same reference axis. Asuitable arrangement for that purpose is represented in FIG. 7b. Thefixture for holding the panel in position, while satisfying thenecessary requirements for mask and panel interchangeability, shouldsimulate a bogey mask and the displacement required of the couplingelements to have the simulated mask engage the panel should alsosimulate the corresponding movement of the coupling element in theactual coupling of a mask to a panel. Since each mounting spring ofamask is secured at one end to the mask and is free at the opposite endwhich has the aperture for engaging the panel stud, the displacement ofthe springs required to effect coupling is essentially a radial orcurvilinear movement rather than a linear one. Consequently, the fixtureof FIG. 7b is arranged to have three coupling elements of identicalconstruction. Each includes a pivoted lever 32 having at one end aconnection to the piston of an air cylinder 31 and carrying at itsopposite end a triangularshaped aperture to engage stud 15 of panel P.When the cylinder is actuated, lever 32 is displaced about a centrallylocated pivot and the aperture is brought along an arcuate or radialpath into engagement with stud is. As explained previously, each suchspring has a minimum two-point contact with its associated stud and thefamily of three springs establishes the necessary six points for theunique positioning desired of panel P. The fixture comprised of thethree levers 32 and their associated cylinders are installed to the endthat the unique position of panel P is one in which its geometric centeris in axial alignment with the geometric center of master pattern M Itis desirable to minimize the weight of the panel to prevent damage toits studs and that may be easily accomplished by the use ofcounter-weight springs (not shown). For example, three springs may bepositioned between the top surface of the exposure table and the freeend of the flange depending from the face panel. These springs are to bedimensioned to have a net load of about one pound on the mounting studs.

ln processing face panel P with green phosphor, a photosensitive coatingincluding particles of green phosphor in suspension is applied as acoating over the entire screen area of the panel and the panel is theninstalled in the exposure chamber by means of the fixture described inthe preceding paragraph. ln screening, as in providing an aperturepattern in mask blank 3,, the nature of the resist employed isdetennined by the character of the exposing energy, that is to say,whether it be light, an electron beam or whatever type of actinic energyis desired to be used. It is most convenient, however, to utilize awater soluble photosensitive resist in screening, such as polyvinylalcohol (pva) sensitized with ammonium dichromate. The slurry coatedpanel having been positioned in the lighthouse is exposed by ultravioletlight through master mask M Since then sensitized coating of the panelcontains green phosphor, the light source for this exposure chamber ispositioned to simulate the electron gun of the tube in process that isassigned to excite the green phosphor dots. Exposure of the panelcreates a latent image of the green phosphor dots, distinguishing theseportions of the resist coating from the remainder thereof by the factthat the exposed elemental areas are rendered insoluble in water. Thepanel is removed from the exposure chamber and washed with water whichdevelops the green phosphor dots on the image area.

The blue and red phosphor dots are established in essentially the sameway but in each case the exposure, for convenience, is made in alight-house that is arranged for a particular color. The lighthouse forblue phosphor processing, for example, has a master pattern M B and itslight source is positioned to represent the blue gun of the tube inprocess. In similar fashion, the lighthouse for processing red phosphorincludes a master pattern M and its light source simulates the electrongun of the tube that is to excite the red phosphor. In the threeexposure and developing steps interlaced deposits of green, blue and redphosphor dots are established on the image area of the face panel of thetube. These deposits are located with great precision over the imagearea by having them exposed to actinic energy through a carefullyprepared master. importantly, in the exposure steps of screening thepanel P is accurately referenced to its screening master rather thanmounting the master within and, therefore, referencing it to the panel.By the same token, mask blank H is referenced to its master in similarfashion during mask exposure and complete interchangeability of masksand panels results.

The screening will be recognized as basically a well-known photoprintingmethod differing in certain important particulars from prior practices.Heretofore, a single mask was used both in screening and in achievingcolor selection in the finished tube. Since the one mask accomplishedboth functions, it was temporarily installed within the face panelsection of the tube in process during the exposure step of each of thethree different phosphors but was otherwise separated from the facepanel during the other process steps required to make a complete screenalthough the mask always traveled with its assigned panel as is thecustom in practicing pairing. in accordance with the present teaching,however, the aperture mask constituting a component of the tube isinstalled within a face-panel section only once, namely, when screeninghas been completed and just prior to sealing the face-panel section to afunnel section in forming the tube envelope. The obvious advantages inthe change include, in addition to interchangeability, minimizedpossibility of damage to masks because their handling is drasticallyreduced and also the mask is kept clean during the tube processing.Another important change is that an exposure mask or master pattern ispermanently installed in each exposure station and the panel isreferenced to the expo sure table and, therefore, to the master ratherthan referencing the master to the panel by installing the master withinthe panel for exposure purposes.

The relative dimensions of the phosphor dots on the screen and theapertures of the mask to be installed in the tube in process aredetermined by the type of tube to be produced. If the tube isconventional, its phosphor dots are dimensioned to be in tangentialcontact with one another and the apertures of the mask are made smallerthan the phosphor deposits so that the electron beams are smaller indimension than the phosphor dots. When a beam is accurately registeredon a phosphor dot, a peripheral portion of the dot is not energized andconstitutes a guard band for assuring white field purity. For theblack-surround of post-deflection-focus tube, however, the obverse sizerelation is adopted and the phosphor dots are, in fact, smaller indiameter than the electron beams. This result of controlled phosphor dotsize is achieved conveniently by suitable dimensioning of the screeningexposure chamber. For example, light source 30 includes a collimator andthe size of its tip may be chosen to control the size of the phosphordots. Other variables that may be adjusted to accomplish the same endinclude the size of the apertures or transparent portions of master M M,or M, as well as the spacing of the master from panel P. It is knownthat when the penumbra effect is utilized in determining phosphor dotsize, some control is available by adjusting the intensity of theexposing light source and/or the duration of the exposure interval. Itis preferred in production, however, to place minimal reliance on thepenumbra effect and to achieve control of phosphor dot size by adjustingthe geometry of the exposure set up, as described. This leads to bettercontrol and more uniformity in the screening process. Of course, for theblacksurround tube it is necessary to surround all of the phosphor dotswith a light-absorbing material which may be accomplished by applyingthe surround material to the screen either before or after the phosphordots have been formed as explained in Fiore et al. US. Pat. No.3,146,368.

In one method of applying light-absorbing material to all portions ofthe screen other than those intended to receive phosphor deposits thescreen is first coated with a clear pva and exposed in the manner ofphosphor dot screening. In this case, however, the exposure anddevelopment establishes dots of clear pva on the screen, instead ofphosphor dots, and if the process is carried out three times, eachelemental screen area designated to receive phosphor will be protectedby clear pva. After the light-absorbing layer has been applied, the pvais removed by a chemical stripper and screening may then proceed in theusual fashion. This procedure, involving three exposures, may besimplified by the present process featuring interchange-ability. For ablack surround tube, the master employed in exposing the clear pva mayhave a pattern designed to expose at one time all of the elemental areasof the screen where the pva is to be retained and thus eliminate twoexposures of the prior art. Such a master may be prepared for example inthe apparatus of FIG. 6a by scanning plate 18 with beams from each ofthe three guns in cluster 23.

After the phosphors have been applied to panel P the screen is filmed inthe usual way and then aluminized to provide for the screen a conductivebacking layer of a diffusely reflective material for optimum brightnessoutput. After aluminizing, the face panel section is ready for maskinsertion and a mask, provided with an aperture pattern processed asdescribed above so as to be precisely related to the pattern of phosphordeposits of the screen, is finally installed in the face panel section.From this point on the processing of the tube is continued inconventional manner, including the panel section with the conical orfunnel envelope section, inserting the cluster ofelectron guns,processing them and so forth.

The master patterns used in processing the mask and in screening neednot be made on substrates of the same material as the shadow mask madefor installation in the tube being fabricated. The substrate materialfor the masters may be metal, plastic or glass. it is selected withthese considerations in mind: it must be readily formed and milled tohave the desired configuration and must be opaque but provided with apattern or transparent portions, such as holes, of accurately controlledlocation, shape and dimension; and must have stability to retain itscharacteristics without alteration either during storage or in use whenpreparing shadow-mask subassemblies or screening the image area of atube in process; and it must be compatible with precise and economicalmethods of duplication, such as contact printing. Presently, thepreference is to planar glass. The shadow mask is chosen with generallythe same considerations but additionally with the requirement that thematerial of the mask be compatible both with tube processing andoperation. Since tube processing and operation involve high temperatureconditions, as in bakeout and in beam scannin the mask has more severerequirements than the master which only has to stand the less rigidconditions of a lighthouse or exposure chamber. Accordingly, the mask isusually made of steel.

A number of benefits provided by the described process have been setforth above and need not be repeated. By adopting only that part of theprocedure that results in interchangeable masks, but not interchangeablepanels, there is a time consuming burden of continuously checking themaster used in screening which is obviously undesirable. Moreover, sincein such a case the master is supported within the panel duringscreening, undesirable limitations are imposed on the material of themaster. For example, it could hardly be constructed of heavy plateglass.

Emphasis may be given to the fact that in the preferred embodiment thescreening master is, in effect, made a part of the exposure chamber.Additionally, it may not be necessary to include a correcting lens inthe optical system of that chamber because the necessary corrections maybe built into the screening master.

While particular embodiments of the invention have been shown anddescribed, it will be obvious to those skilled in the art that changesand modifications may be made without departing from the invention inits broader aspects, and, therefore, the aim in the appended claims isto cover all such changes and modifications as fall within the truespirit and scope of the invention.

I claim: 1. in the manufacture of a shadow-mask type of color cathoderaytube having a face panel section, the improvement which includes thefollowing steps:

forming a mask-frame component comprising an imperforate mask portion ofa material subject to etching configured to correspond substantially tothe internal surface of said face panel section of the tube in processand further comprising a frame portion extending from said mask portionfor securing the mask-frame component in a predetermined position withinsaid face panel section;

applying to at least one surface of said mask portion a coat ing of asensitized resist;

supporting said mask-frame component in predetermined alignment withreference to a first master having a predetermined pattern oftransparent portions by an arrangement establishing at least six pointsof coupling between said mask-frame and said master to support saidmask-frame and said master with their geometric centers aligned along acommon reference axis;

exposing said coating to actinic energy through said master to establishin said coating a latent image of a desired aperture pattern;

developing said image and thereafter etching said mask portion to createtherein said aperture pattern;

and producing a screened face panel from a screening master having apredetermined relationship to said first master so that any aperturemask processed from said first master is utilizable with any face panelprocessed from said screening master.

2. The improvement in accordance with claim 1 in which said mask portionand said frame portion are separately formed;

and said mask portion is stress relieved and then is united with saidframe portion.

3. The improvement in accordance with claim 2 in which said mask-framecomponent is further stress relieved after said mask portion and saidframe portion have been united to one another.

4. The improvement in accordance with claim 3 in which said mask portionand said frame portion are oxidized prior to the application of saidresist coating;

and in which said mask is treated with an oxide stripper subsequent tosaid development step but prior to said etching step.

5. The improvement in accordance with claim 3 in which said frameportion is provided with leaf mounting springs and is stress relievedbefore being united with said mask portion.

6. The improvement in accordance with claim 1 in which a coating of saidsensitized resist is applied to both surfaces of said mask portion;

said mask-frame component is supported in predetermined alignment with apair of first masters positioned on opposite sides of said mask-framecomponent;

both coatings of resist are exposed through said pair of masters,respectively to establish said latent image;

said mask portion is etched from both sides to create said aperturepattern;

and said screening master has a predetermined relationship to one ofsaid first masters.

7. The improvement in accordance with claim 6 in which saidpredetermined alignment is established by six point couplingarrangements which support said mask-frame component and both of saidmasters with their geometric centers aligned along a common referenceaxis.

8. The improvement in accordance with claim 7 in which said pair ofmasters is formed by a photoprinting process in which:

a. a bogey mask-frame is positioned in said predetermined alignmentbetween a pair of substrates having sensitized surfaces facing saidbogey mask-frame and (b) both of said surfaces are exposed to actinicenergy directed thereto through said bogey mask frame.

9. The improvement in accordance with claim 1 which includes thefollowing additional steps:

developing said screening master to have a preselected relationship tosaid first master through which said exposure step of said mask-frametakes place;

supporting said face panel referenced to said screening master inaccordance with said predetermined alignment of said mask-framecomponent in relation to said first master;

and screening on said face panel a phosphor pattern determined byexposing said panel through said screening master.

10. The improvement in accordance with claim 9 in which said screeningmaster is derived from the same bogey maskframe used in developing saidfirst master.

1]. The improvement in accordance with claim it) in which said aperturepattern of said mask-frame is a multiplicity of substantially circularholes distributed over a generally rectangular field;

in which a family of three screening masters are developed from saidbogey mask-frame, one for screening with each of green, blue and redemitting phosphors;

and in which said face panel is successively screened with each of saidthree screening masters to form a phosphordot triad screen on saidpanel.

12. The improvement in accordance with claim 11 in which said mask-framecomponent is installed within said face panel only after said panel hasbeen screened through said three screening masters.

13. The improvement in accordance with claim 11 in which the screeningof said face panel with any of said phosphors includes the step ofremovably supporting said panel in an exposure chamber in which the oneof said screening masters associated with the phosphor being screened ispermanently installed;

and in which said panel is referenced to said screening master in themanner in which said mask-frame component is referenced to its masterduring the exposure of said mask portion.

14. The improvement in accordance with claim 13 in which said screeningmaster is derived from said bogey mask-frame through a process whichincorporates correction factors in the pattern of said screen masterwhich may be projected directly on said panel, without the imposition ofa correcting lens, in the exposure of said panel.

15. In the manufacture of a shadow mask color tube, the improvementswhich includes the following steps:

forming a mask-frame having a mask portion of a material subject toattack by an etchant and characterized by the fact that the mask is aformed imperforate blank;

coating said mask with a sensitized resist;

supporting said mask-frame by an arrangement establishing at least sixpoints of coupling between said mask-frame and a fixture with thegeometric center of said mask disposed along a first reference axis;

similarly supporting a first master, representing the aperture patternof a bogey mask-frame, by an arrangement establishing at least sixpoints of coupling between said first master and said fixture with thegeometric center of said first master on said first reference axis;

exposing said mask to actinic energy through said first master to createa latent image of an aperture pattern in said coating;

developing said latent image and then etching said mask to create saidaperture pattern therein;

screening the face panel of said tube by:

a. coating the internal surface of the face panel with a sensitizedresist;

b. supporting said panel by an arrangement establishing at least sixpoints of coupling between said panel and another fixture so that thegeometric center of said panel is disposed along a second referenceaxis;

c. similarly supporting a screening master, also represent ing theaperture pattern of said bogey mask-frame, by an arrangementestablishing at least six points of coupling between said screeningmaster and said other fixture with the geometric center of saidscreening master on said second reference axis, said second axis beingequivalent to said first axis in that said first master and saidscreening master are both referenced to said bogey mask-frame; and

d. applying to said panel a phosphor pattern determined by exposing saidpanel to actinic energy through said screening master;

and finally installing said mask-frame in said panel. 7 16. Theimprovement in accordance with claim 15 in which both surfaces of saidmask are coated with said resist;

a second master is supported as said first master but on the oppositeside of said mask; both surfaces of said mask are exposed through saidfirst and second masters, respectively, to create said latent image; andsaid panel is screened with green, blue and red emitting phosphorsthrough repeating said steps (a) (d) three times but each time utilizinga screening master derived from said bogey mask frame and individual toan assigned one of said phosphors. 17. The improvement in accordancewith claim 15 in which said mask-frame is stress relieved before beingexposed to actinic energy.

1. In the manufacture of a shadow-mask type of color cathode-ray tubehaving a face panel section, the improvement which includes thefollowing steps: forming a mask-frame component comprising animperforate mask portion of a material subject to etching configured tocorrespond substantially to the internal surface of said face panelsection of the tube in process and further comprising a frame portionextending from said mask portion for securing the mask-frame componentin a predetermined position within said face panel section; applying toat least one surface of said mask portion a coating of a sensitizedresist; supporting said mask-frame component in predetermined alignmentwith reference to a first master having a predetermined pattern oftransparent portions by an arrangement establishing at least six pointsof coupling between said mask-frame and said master to suppOrt saidmask-frame and said master with their geometric centers aligned along acommon reference axis; exposing said coating to actinic energy throughsaid master to establish in said coating a latent image of a desiredaperture pattern; developing said image and thereafter etching said maskportion to create therein said aperture pattern; and producing ascreened face panel from a screening master having a predeterminedrelationship to said first master so that any aperture mask processedfrom said first master is utilizable with any face panel processed fromsaid screening master.
 2. The improvement in accordance with claim 1 inwhich said mask portion and said frame portion are separately formed;and said mask portion is stress relieved and then is united with saidframe portion.
 3. The improvement in accordance with claim 2 in whichsaid mask-frame component is further stress relieved after said maskportion and said frame portion have been united to one another.
 4. Theimprovement in accordance with claim 3 in which said mask portion andsaid frame portion are oxidized prior to the application of said resistcoating; and in which said mask is treated with an oxide strippersubsequent to said development step but prior to said etching step. 5.The improvement in accordance with claim 3 in which said frame portionis provided with leaf mounting springs and is stress relieved beforebeing united with said mask portion.
 6. The improvement in accordancewith claim 1 in which a coating of said sensitized resist is applied toboth surfaces of said mask portion; said mask-frame component issupported in predetermined alignment with a pair of first masterspositioned on opposite sides of said mask-frame component; both coatingsof resist are exposed through said pair of masters, respectively toestablish said latent image; said mask portion is etched from both sidesto create said aperture pattern; and said screening master has apredetermined relationship to one of said first masters.
 7. Theimprovement in accordance with claim 6 in which said predeterminedalignment is established by six point coupling arrangements whichsupport said mask-frame component and both of said masters with theirgeometric centers aligned along a common reference axis.
 8. Theimprovement in accordance with claim 7 in which said pair of masters isformed by a photoprinting process in which: a. a bogey mask-frame ispositioned in said predetermined alignment between a pair of substrateshaving sensitized surfaces facing said bogey mask-frame and (b) both ofsaid surfaces are exposed to actinic energy directed thereto throughsaid bogey mask frame.
 9. The improvement in accordance with claim 1which includes the following additional steps: developing said screeningmaster to have a preselected relationship to said first master throughwhich said exposure step of said mask-frame takes place; supporting saidface panel referenced to said screening master in accordance with saidpredetermined alignment of said mask-frame component in relation to saidfirst master; and screening on said face panel a phosphor patterndetermined by exposing said panel through said screening master.
 10. Theimprovement in accordance with claim 9 in which said screening master isderived from the same bogey mask-frame used in developing said firstmaster.
 11. The improvement in accordance with claim 10 in which saidaperture pattern of said mask-frame is a multiplicity of substantiallycircular holes distributed over a generally rectangular field; in whicha family of three screening masters are developed from said bogeymask-frame, one for screening with each of green, blue and red emittingphosphors; and in which said face panel is successively screened witheach of said three screening masters to form a phosphor-dot triad screenon said panel.
 12. The improvement in accordance with claim 11 in whichsaid mask-frame compOnent is installed within said face panel only aftersaid panel has been screened through said three screening masters. 13.The improvement in accordance with claim 11 in which the screening ofsaid face panel with any of said phosphors includes the step ofremovably supporting said panel in an exposure chamber in which the oneof said screening masters associated with the phosphor being screened ispermanently installed; and in which said panel is referenced to saidscreening master in the manner in which said mask-frame component isreferenced to its master during the exposure of said mask portion. 14.The improvement in accordance with claim 13 in which said screeningmaster is derived from said bogey mask-frame through a process whichincorporates correction factors in the pattern of said screen masterwhich may be projected directly on said panel, without the imposition ofa correcting lens, in the exposure of said panel.
 15. In the manufactureof a shadow mask color tube, the improvements which includes thefollowing steps: forming a mask-frame having a mask portion of amaterial subject to attack by an etchant and characterized by the factthat the mask is a formed imperforate blank; coating said mask with asensitized resist; supporting said mask-frame by an arrangementestablishing at least six points of coupling between said mask-frame anda fixture with the geometric center of said mask disposed along a firstreference axis; similarly supporting a first master, representing theaperture pattern of a bogey mask-frame, by an arrangement establishingat least six points of coupling between said first master and saidfixture with the geometric center of said first master on said firstreference axis; exposing said mask to actinic energy through said firstmaster to create a latent image of an aperture pattern in said coating;developing said latent image and then etching said mask to create saidaperture pattern therein; screening the face panel of said tube by: a.coating the internal surface of the face panel with a sensitized resist;b. supporting said panel by an arrangement establishing at least sixpoints of coupling between said panel and another fixture so that thegeometric center of said panel is disposed along a second referenceaxis; c. similarly supporting a screening master, also representing theaperture pattern of said bogey mask-frame, by an arrangementestablishing at least six points of coupling between said screeningmaster and said other fixture with the geometric center of saidscreening master on said second reference axis, said second axis beingequivalent to said first axis in that said first master and saidscreening master are both referenced to said bogey mask-frame; and d.applying to said panel a phosphor pattern determined by exposing saidpanel to actinic energy through said screening master; and finallyinstalling said mask-frame in said panel.
 16. The improvement inaccordance with claim 15 in which both surfaces of said mask are coatedwith said resist; a second master is supported as said first master buton the opposite side of said mask; both surfaces of said mask areexposed through said first and second masters, respectively, to createsaid latent image; and said panel is screened with green, blue and redemitting phosphors through repeating said steps (a) - (d) three timesbut each time utilizing a screening master derived from said bogey maskframe and individual to an assigned one of said phosphors.
 17. Theimprovement in accordance with claim 15 in which said mask-frame isstress relieved before being exposed to actinic energy.